The last win32 version I'd tested with was a bit ago
@ in 5.14 and it didn't have this problem.

Sorry - I couldn't work out what it is that you're asking about.

And I couldn't spot anything in the testers report that indicates any
problem with any of the paths.
Both "\" and "/" are acceptable (and essentially equivalent) where used
(AFAICS).

If you do:
$test = "C:\this";
what do you expect to be output by:
printf "%s\n", $test;
And if you do:
$^X = "C:\Strawberry\perl\bin\perl.exe";
what do you expect to be output by:
printf "5.20 path for perl: $^X???\n";
Cheers,